The need for joining or affixing dissimilar materials is in widespread existence, as the difference in properties of the materials are needed, such as a glass window for transparency affixed to a metal frame for support and strength, or a corrosion resistant material such as copper that is soft being affixed to a steel structure for strength, or a paint affixed to a resilient material such as a car bumper, or a chrome plating on a plastic material for appearance, or weight savings, or cost savings, and the like. Thus the want or need for affixing dissimilar materials outweighs the problems that affixing dissimilar materials causes. Thus this whole need or desire to join dissimilar materials stems from generally wanting to tailor engineer properties, for instance a particular part needing a high or low temperature resistance in a particular area (i.e. a temperature probe), or corrosion resistance in a certain area (i.e. a boat hull), abrasion or wear resistance in a certain area (i.e. a gear), or in electronics affixing of a non-conductive material to a conductive material (i.e. semiconductor chips, batteries), as just a few examples.
The range of dissimilarity is key to understand in solving the problem of affixing materials, such that slightly dissimilar materials would be basically alike materials with minor differences, such as two different types of steels or a variation within a material category such as affixing two different types of aluminum together. Next on the dissimilarity scale would be dissimilar materials such as steel to copper. For the highest level of dissimilarity of affixing materials would be two completely different material compositions, such as a ceramic material to metal or an organic material to metal. Thus the highly dissimilar material affixing presents the highest challenge as the interface of the highly dissimilar materials are subject to dramatic reactive differences in the two materials to various environmental conditions. As an example, for a ceramic material to a metal, wherein when these two materials are exposed to an environmental temperature change, the steel will move greatly relative to the ceramic causing this relative movement to have to be accommodated in whatever structure is used for the affixment, i.e. rivets, bolts, adhesives, interference fits, threads, welding, and the like, or else failure of the affixment will occur.
For the highest material dissimilarity situation, for instance steel to ceramic, the options are more limited, as certainly welding is not an option due to great dissimilarity in material melting temperatures, i.e. such that welding really requires that the materials be in the slightly dissimilar category, then looking at mechanical fastening could be a possibility (bolts, threads, rivets, etc.), however, the holes that the mechanical fastening requires can have added problems of causing stress points, also selected the material of the fasteners themselves can be challenging, plus due to the size and configuration of the parts to be affixed to one another, mechanical fastening may not be a good option. This leaves adhesives that can overcome the problems of welding and mechanical fasteners, however, causing a few of their own issues, such as bonding of the adhesive to the material, and material properties of the adhesive itself for temperature, corrosion, shear and tensile strength.
However, the wide ease of application (relative to welding and mechanical fastening) and the ability to accommodate the most difficult of highly dissimilar material affixing makes adhesives attractive to use, plus there are ever expanding options for different types of adhesives, also adhesives have a small weight component (relative to welding and mechanical fastening) and can distribute loading as between the materials in a more distributed manner again (relative to welding and mechanical fastening). Drawbacks of adhesives are the permanent affixment, thus making disassembly only available via causing material damage (much the same as welding), also environmental conditions, such as temperature, corrosives, aging, and the like can operate to change the bonding characteristics of the adhesive leading to dissimilar material separation-sometimes this can happen rather suddenly as opposed to a gradual dissimilar material separation, which would normally be preferred in a failure mode, in addition an adhesive requirement of meticulous surface preparation of the dissimilar materials to be affixed can be critical in the adhesive bonding property. Thus adhesives while favored are not perfect for affixing dissimilar materials due to the above mentioned issues with adhesives in affixing dissimilar materials.
Looking at the prior art related to dissimilar material affixing, particularly concerning semiconductor chips, in U.S. Pat. No. 4,356,047 to Gordon et al., disclosed is a ceramic lid assembly that includes an integral heat fusible layer defining a hermetic sealing area provided around the periphery of a ceramic lid for hermetic sealing of semiconductor chips in a flat pack that acts to protect the chip internal components. In Gordon, the integral heat fusible layer includes a metallized layer, an oxidation inhibiting layer, and a pre-flowed solderable layer in registration with each other in the hermetic sealing area, wherein the lid is of substantially non-conductive or dielectric material having a thickness range of from 0.010-0.040 inch. As stated in Gordon, ceramic material is generally preferred as it is inexpensive, easily metallized and has a coefficient of thermal expansion which matches that of the semiconductor flat pack, thus ceramic material found suitable includes the oxides of aluminum, beryllium, and magnesium. Gordon had discovered that single crystal sapphire is ideally suited for use as a lid in hermetic sealing of EPROMs by being transparent to ultra-violet light and the use of single crystal sapphire provides a large window opening for easy accessibility to the semiconductor chip for erasing and programming the Read Only Memory, see; abstract, column 3, lines 39-56. Thus, in Gordon, the affixment of the ceramic in the form of sapphire to bond at the outer periphery via a wettable metal layer with a metallized layer to heat fuse the ceramic lid to the flat pack for a hermetic seal is utilized.
Continuing in the prior art related to dissimilar material affixing, particularly in affixing an insulator surface with a conductive surface, in U.S. Pat. No. 4,457,972 to Griffith et al., disclosed is an enhanced adhesion by high energy bombardment. Wherein Griffith has films of gold, copper, silicon nitride, or other materials that are firmly bonded to insulator substrates such as silica, a ferrite, or Teflon (polytetrafluoroethylene) by irradiating the interface with high energy ions. Apparently, according to Griffith, track forming processes in the electronic stopping region cause intermixing in a thin surface layer resulting in improved adhesion without excessive doping (meaning surface material property changes), thus the high energy facilitates thick layers that can be bonded by depositing or doping the interfacial surfaces with fissionable elements or alpha emitters. Griffith states that the substrates were commercial grade Teflon, sapphire, nickel-zinc ferrite, fused quartz and soda-lime glass, with the substrates being cleaned with trichloroethylene, nitric acid and methanol before being loaded into a diffusion-pumped evaporator, wherein 200 to 500 Angstrom thick films of gold or copper were evaporated onto the substrates in a vacuum of 1 times 10 to the negative sixth power Torr., wherein silicon tetra nitrogen films on silicon were formed by sputter deposition in an RF discharge sputtering chamber. According to Griffith, after irradiation the adhesion of the films, they were tested by means of the “Scotch Tape Test”: wherein a piece of tape was firmly pressed on the irradiated surface and slowly peeled off by hand, with the adhesion effect obtained after the high energy bombardment is so dramatic that more quantitative tests of adhesion were not necessary. Griffith primarily is applied to enhanced bonding with Aluminum on Teflon; see abstract, column 5, lines 22-38.
Further looking at the prior art related to dissimilar material affixing, again particularly concerning semiconductor chips, in U.S. Pat. No. 4,939,101 to Black, et al., disclosed are foregoing objects that are accomplished by cleaning the wafer surfaces to be bonded, being in particular silicon on sapphire, placing the wafer surfaces to be bonded in contact, annealing the bonded wafers at an elevated temperature to seal the interface and then further annealing the wafers at an elevated temperature in the presence of a hydrostatic pressure in excess of 300 psi. Black has in one embodiment; the hydrostatic pressure being up to about 15,000 psi, wherein the high temperature/high pressure annealing eliminates voids at the bonded interface thereby leaving a void free bonded interface. According to Black the benefit of semiconductor-on-insulator (SOI) devices are because the high isolation provided between adjacent devices by the insulating substrate.
What is needed is a structure and method of affixing a ceramic to a steel that does not require excessive heat or pressure nor a convoluted surface configuration of the ceramic that could add stress risers to the ceramic piece wherein the ceramic piece and the steel piece are each cylindrical in shape utilizing an adhesive as a bonding material as between the ceramic and the steel, wherein a primary separating force between the ceramic and the steel would be in shear, thus placing the adhesive in shear, wherein further requirements would be that the adhesive is of a medical grade and is capable of withstanding multiple cycles of heat sterilization.